Reservoir built-in type actuator

Abstract

A stand pipe is disposed so as to be fitted with the inner periphery surface of a piston rod with a hollow structure and a reservoir is incorporated into the inside of the stand pipe, whereby it becomes possible to reduce the size of an EHA device. Besides, since the reservoir is separated from both an annulus-side oil chamber and a bore-side oil chamber, a stable reservoir performance can be exhibited without being influenced by a fluid pressure resulting from an external force. Moreover, as a result of installation of the stand pipe, a difference between the amount of fluid required per unit stroke in the annulus-side oil chamber and that in the bore-side oil chamber becomes smaller, so that the required volume of the reservoir oil chamber can be reduced and it is possible to constitute an efficient EHA device with little difference between the energy consumption during compressing and that during extending. Consequently, it is possible to provide a reservoir built-in type actuator capable of exhibiting a stable performance without being influenced by an external force acting on the actuator and capable of attaining the reduction in size of the entire EHA device.

1. An actuator in which a cylinder type actuator body and a piston having a piston rod with a hollow structure adapted to slide through the interior of the cylinder of said actuator body are included, comprising:
 a motor; 
 a pump for the supply of fluid in accordance with revolutions of said motor; 
 a controller for controlling revolutions of said motor in accordance with movement of said piston; and 
 a reservoir for adjusting the amount of fluid to be supplied in accordance with a flow rate difference induced with movement of said piston, wherein a stand pipe is disposed so as to be fitted with the inner periphery surface of said piston rod and said reservoir is incorporated into the inside of said stand pipe. 
 
   
   
     2. The reservoir built-in type actuator according to  claim 1 , wherein:
 said cylinder is constructed to have an annulus-side oil chamber to which fluid is supplied when said cylinder performs a compressing movement and a bore-side oil chamber to which fluid is supplied when said cylinder performs an extending movement; and 
 said reservoir is separated from both said annulus-side oil chamber and said bore-side oil chamber and is connected thereto through fluid pipes. 
 
   
   
     3. The reservoir built-in type actuator according to  claim 1 , wherein said reservoir is constructed to have a double structure comprising a reservoir oil chamber for the storage of fluid and an elastic support portion partitioned by a free piston, said elastic support portion having a coiled spring as an elastic support member. 
   
   
     4. The reservoir built-in type actuator according to  claim 2 , wherein said reservoir is constructed to have a double structure comprising a reservoir oil chamber for the storage of fluid and an elastic support portion partitioned by a free piston, said elastic support portion having a coiled spring as an elastic support member.